[8.8](backport #36091) Pin PyYAML version to 5.3.1 to avoid CI errors temporarily

[mergify]

This is an automatic backport of pull request #36091 done by Mergify.
Cherry-pick of 46adbac has failed:

On branch mergify/bp/8.8/pr-36091
Your branch is up to date with 'origin/8.8'.

You are currently cherry-picking commit 46adbacfb5.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   CHANGELOG-developer.next.asciidoc
	modified:   metricbeat/Dockerfile
	modified:   metricbeat/module/kubernetes/_meta/terraform/eks/requirements.txt

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   libbeat/tests/system/requirements.txt
	both modified:   libbeat/tests/system/requirements_aix.txt

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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• Start Time: 2023-08-01T06:09:33.386+0000

• Duration: 83 min 4 sec

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Test	Results
Failed	0
Passed	25844
Skipped	1835
Total	27679

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